The present invention relates to a post-processing apparatus, sheet ejection method thereof and image forming system.
One of the proposals having been made so far is a post-processing apparatus wherein, when a certain number of sheets have been ejected to a sheet ejection tray, the sheet ejection tray is lowered in response to it, and when the sheets on the sheet ejection tray have been removed, the lowered sheet ejection tray rises to the initial position. In this post-processing apparatus, the sheets are ejected to the staple tray arranged inside a post-processing apparatus to ensure that the sheets are not ejected to the upward traveling sheet ejection tray when printing operation is performed during the upward travel of the sheet ejection tray. After the upward travel of the sheet ejection tray, the sheets on the staple tray are ejected to the sheet ejection tray. If the sheets having been printed are ejected to the upward traveling sheet ejection tray, sheets might be put in disorder since the sheet ejection tray is moving upward. However, this arrangement prevents such a trouble (Japanese Unexamined Patent Application Publication No. Hei 10 (1998)-139255.
In an image forming apparatus having been proposed, buttons are provided to correspond to a plurality of sheet ejection trays, respectively, and the destination of the sheets is changed to the sheet ejection tray corresponding to the button having been pressed. During the operation, there may be the cases where sheets are stacked incorrectly on the sheet ejection tray and are misaligned to cause the ejected sheets being scattered due to some failure having occurred on the sheet ejection tray. If such a trouble occurs, however, in this image forming apparatus, the sheet ejection tray is changed by pressing the button. This operation prevents the sheets from being scattered, without the printing operation being stopped (Japanese Unexamined Patent Application Publication No. 2004-59268).
In the apparatus disclosed in the Japanese Unexamined Patent Application Publication No. Hei 10 (1998)-139255, if the sheets already stacked on the sheet ejection tray are to be removed during the printing operation, stacking failure or sheet jamming may occur due to the possible contact between the sheets to be removed and the sheets to be ejected.
In the case of the apparatus disclosed in the Japanese Unexamined Patent Application Publication No. 2004-59268, the sheet ejection tray as a destination of sheet ejection can be changed by pressing the button. Thus, if the sheet ejection tray as the destination of sheet ejection is changed, there is no possibility of contact between the sheets to be removed and the sheets to be ejected. Thus when removing the sheets stacked on the sheet ejection tray, there is no possibility of stacking failure or paper jamming. However, in the apparatus described in the Japanese Unexamined Patent Application Publication No. 2004-59268, sheets are ejected to a plurality of sheet ejection trays. Thus, the regularity of the pages may be lost when the user tries to rearrange the sheets having been removed, depending on how sheets are stacked. To put it more specifically, when the destination of sheets has been changed in the order of the sheet ejection tray 1, sheet ejection tray 2, and sheet ejection tray 3, the regularity of the pages will be lost if sheets are stacked by the user in the order of the sheet ejection tray 1, sheet ejection tray 3 and sheet ejection tray 2.
In the general post-processing apparatus, such post-processing operations as stapling and shifting can be performed only when sheets are ejected to the sheet ejection tray as a main ejection tray for the reason of mechanism. Thus, if the sheet ejection tray is changed as in the case of the Japanese Unexamined Patent Application Publication No. 2004-59268, the destination of sheet ejection may be changed from the main sheet ejection tray to the subsidiary sheet ejection tray. In this case, restrictions will be imposed on the post-processing function.
In view of the problems described above, it is an object of the present invention to provide a post-processing apparatus, sheet ejection method thereof and image forming system wherein, when sheets stacked on the sheet ejection tray are to be removed, the possibility for stacking failure or paper jamming is eliminated, page regularity is ensured, and restrictions are not imposed on post-processing functions.